Update reader.c

fix PyPy, maybe cpyext problem

Fatal error in cpyext, CPython compatibility layer, calling PyList_CheckExact
Either report a bug or consider not using this particular extension
<OpErrFmt object at 0x7fcd65f15d10>
RPython traceback:
  File "pypy_module_cpyext_api.c", line 11944, in PyList_CheckExact
  File "pypy_module_cpyext_pyobject.c", line 1061, in BaseCpyTypedescr_realize
  File "pypy_objspace_std_objspace.c", line 3590, in allocate_instance__W_ObjectObject
  File "pypy_objspace_std_typeobject.c", line 3749, in W_TypeObject_check_user_subclass
Segmentation fault